Improve mktime cache #101
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Improve mktime cache #101
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…t present If the timestamp is not actually there in the message, we still tried to call convert_and_normalize_wall_clock_time_to_unix_time_with_tz_hint(), which in turn calls mktime(), which is a heavyweight operation. Let's not do that. Signed-off-by: Balazs Scheidler <balazs.scheidler@axoflow.com>
Without this patch, cached_mktime() produces a cached value for every second, and would call mktime() again as the second changes. This can be problematic when timestamps are parsed from different seconds in succession (e.g. when the syslog timestamp is 1 second away from a timestamp being parsed using strptime or date-parser). In these cases the cache was invalidated and mktime() was called again. mktime() is _slow_ as it even calls tzset() and validates that /etc/localtime is still pointing to the same timezone. This patch changes the caching strategy: - instead of specific seconds we calculate the cached value for the top of the hour (e.g. minutes==seconds==0) - timezones never change within the same hour, so as long as we are trying to use the cached value, we will do so as long as the year/month/day/hour value matches (plus isdst) - with this, mktime() will be called once every hour. If there's some fluctuation between subsequent timestamps at the turn of the hour, we can still exhibit limited caching (e.g. subsequent timestamps from the last hour and this one), but this is a lot better than the existing behaviour where we do that for every second. Signed-off-by: Balazs Scheidler <balazs.scheidler@axoflow.com>
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May 22, 2024
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This improves the caching in cached_mktime() so that a single real mktime() invocation is valid for up to an hour.